1. Field of the Invention
The present invention relates to a magnetic head unit having a thin-film type magnetic head used for a magnetic disk apparatus.
2. Description of the Related Art
Recently, in conventional magnetic disk apparatuses, monolithic type magnetic heads have been replaced with thin-film type magnetic heads.
FIG. 1A is an exploded view of an example of a magnetic head unit having the thin-film type magnetic head used for the conventional magnetic disk apparatuses. FIG. 1B is an exploded view of a part of the magnetic head unit shown in FIG. 1A. In the present specification, the magnetic head unit refers to an assembly of a spring arm having a magnetic head mounted on an end of the spring arm. The other end of the spring arm is adapted to be mounted on a member of a magnetic head positioning mechanism.
Referring now to FIG. 1A, one end (a base portion 1a) of a spring arm 1 formed of an elastic plate is mounted to a member of a magnetic head positioning mechanism (not shown in the figure) via a plate-like spacer 2. A gimbal 3 is mounted on another end 1b of the spring arm 1. The gimbal 3 is mounted, as shown in FIG. 1B, on the spring arm 1 by means of laser welding at positions indicated by x. A core slider 4 of a magnetic head h is mounted by adhesive on the gimbal 3.
Two magnetic head elements 5 are formed on a rear side surface of the magnetic head, the magnetic head elements 5 being connected by lead wires 6 which lead to a read wire 8 covered with an insulating tube 7 fixed to the spring arm 1. The lead wire 8 is lead to a recording/reproducing circuit 9 shown in FIG. 2.
The spring arm 1 is slightly bent near the base portion 1a so that a bent portion 1c is formed so as to generate a spring force.
FIG. 2 is an exploded view of a conventional magnetic disk apparatus in which two magnetic head units shown in FIG. 1A are used.
Two magnetic head units are mounted on a driving arm 13 which pivots about an axis 12 so that a magnetic disk 10 accommodated inside the magnetic head apparatus is sandwiched between two of the core sliders 4 mounted on the respective spring arms 1. Each of the core sliders 4 is pressed to a respective surface of the magnetic disk 10 by the spring force generated by the bent portion 1c.
When the magnetic disk 10 is rotated at a high speed, the magnetic heads h float, if the magnetic heads h are of the floating type, on the respective surface of the magnetic disk 10 due to an air flow generated by the rotation of the magnetic disk 10. If the magnetic heads h are contact type magnetic heads, the magnetic heads h do not float, but instead slide on the respective surfaces of the magnetic disk 10. The magnetic heads h are moved to respective target tracks on the surfaces of the magnetic disk 10 by pivoting the spring arms about the axis 12.
FIG. 3 is a perspective view of a thin-film type magnetic head. FIG. 4 is an enlarged cross sectional view of the thin-film type magnetic head shown in FIG. 3 taken along a line 4--4 of FIG. 3.
The thin-film type magnetic head shown in FIG. 3 comprises the slider 4 and head elements 5. The head elements 5 are formed by means of a film deposition technique and lithography. Terminals 15a and 15b for recording/reproducing coils are provided near the head elements 5.
Each of the head elements 5 comprises a lower magnetic pole 16, an upper magnetic pole 17 and a thin-film coil 19 wound around a connecting portion 18 between the lower magnetic pole 16 and the upper magnetic pole 17. A gap insulating layer 20 is provided between the lower magnetic pole 16 and the upper magnetic pole 17 so that a gap G having a predetermined width is formed between the two poles. The gap G faces the surface of the magnetic disk 10 to perform a magnetic recording/reproducing operation.
In the construction of the magnetic head unit shown in FIG. 1 in which the lead wire 8 is covered with the insulating tube 7, the insulating tube 7 occupies a relatively large space to prevent miniaturization of the magnetic disk apparatus. Additionally, the insulating tube 7 makes an assembling operation difficult, particularly an automated assembling operation. Further, there is a strong possibility that the lead wire 8 will pick up noises, resulting in degradation of an S/N ratio of a signal sent via the lead wire 8.
In order to eliminate the above-mentioned problems, a method for forming a signal transmitting line on a spring arm is suggested in Japanese Laid-Open Patent Application No. 4-21918. In the method, a signal line is formed of a pattern of a conductive layer on an insulating layer formed on the spring arm. However, the method has a problem in that the signal transmitting line formed of the conductive layer is easily damaged or broken during a process for forming the bent portion 1c shown in FIG. 1A
Japanese Laid-Open Patent Application No. 4-111217 discloses a magnetic head unit in which a flexible printed circuit board is attached to a spring arm, and a portion of the flexible circuit board corresponding to the above of the spring arm bent portion is not adhered to the spring arm. Instead, in this construction, the portion of the flexible printed circuit board corresponding to the bent portion of the spring arm is free, and thus the there is no bending stress applied to the flexible printed circuit board. However, this construction cannot be applied to a highly miniaturized spring arm such as a spring arm having a thickness of a few microns and a 4.6 mm width.
There is another problem in that the ability of the insulating layers 21 and 22 of the magnetic head element 5 to withstand dielectric voltage is very low because they each have a thickness of only 1 to a few microns. Accordingly, if a relatively high voltage of about 100 V or more is applied between the thin-film coil 19 and the poles 16 and 17 due to a generation of static electricity, the insulating layers 21 and 22 may be easily damaged due to electric discharge.
If the insulation between the thin-film coil 19 and the poles 16 or 17 is damaged, an electric discharge may occur between the core slider, which is made of a conductive material such as Al.sub.2 O.sub.3 TiC, and the magnetic poles 16 or 17, resulting in the gap G or the floating surface of the core slider 4 being damaged. Additionally, when the magnetic disk apparatus is in operation, an electric discharge may occur between the magnetic disk 10 and the magnetic poles 16 or 17, resulting in the magnetic gap G being damaged. When the core slider 4 is damaged, the floating characteristic of the magnetic head is deteriorated, which condition causes a generation of noises in the recording/reproducing signal. If the magnetic head is a contact type head, the damaged surface of the magnetic head may scratch the magnetic disk 10.
Problems similar to the above-mentioned problems may occur when the core slider is miniaturized. That is, when the magnetic head is heated, the magnetic head tends to expand due to thermal expansion, but a portion of the core slider attached to the gimbal or the spring arm by adhesive cannot expand in accordance with the expansion of the magnetic head. This creates bending of the core slider, and thus the floating characteristic of the magnetic head may be deteriorated.